Organic light emitting display and driving method thereof

ABSTRACT

Disclosed are an organic light emitting display capable of preventing lowering of brightness and prolonging its a lifespan, and a driving method thereof. The organic light emitting display controls a level of a gate signal, by outputting a gate high voltage after controlling a level of the gate high voltage, according to a level of a threshold voltage sensed from each pixel of a display panel.

CROSS-REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S.C. §119(a), this application claims the benefit ofearlier filing date and right of priority to Korean Application No.10-2013-0157565, filed on Dec. 17, 2013, the contents of which isincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This specification relates to an organic light emitting display, andmore particularly, an organic light emitting display capable ofpreventing brightness reduction by compensating for degradation of adevice due to change of a threshold voltage, and a driving methodthereof.

2. Background of the Invention

As information society develops, demands for display devices fordisplaying images increase in various manners. Recently, various flatdisplay devices such as liquid crystal displays (LCDs), plasma displaypanels (PDPs), and organic light emitting diodes (OLEDs) are beingutilized.

Among such flat display devices, the OLEDs have advantages such as a lowvoltage driving, a thin thickness, an excellent viewing angle, and afast response speed. As the OLEDs, active matrix type OLEDs fordisplaying images as pixels are arranged in the form of matrices arebeing widely used.

FIG. 1 is a view illustrating a configuration of an organic lightemitting display in accordance with the related art, and FIG. 2 is anequivalent circuit diagram with respect to a single pixel of FIG. 1.

Referring to the drawings, the related art organic light emittingdisplay 1 includes a display panel 2, a timing controller 3, a drivingvoltage generator 4, a gate driving unit 5, and a data driving unit 6.

The display panel 2 is configured to display images, and a plurality ofgate lines (GL1˜GLn) and a plurality of data lines (DL1˜DLm) fordefining pixel regions by crossing each other are formed at the displaypanel 2.

As shown in FIG. 2, a pixel (P) is formed at each pixel region. Thepixel (P) includes a switching transistor (ST), a capacitor (C), adriving transistor (DR) and an organic light emitting diode (OLED) eachformed between a gate line (GL1) and a data line (DL1). Each transistor(ST, DR) is a thin film transistor (TFT) formed of amorphous silicon(a-Si:H).

The switching transistor (ST) of the pixel (P) may have a gate electrodeconnected to a gate line (GL1), a source electrode connected to a dataline (DL1), and a drain electrode connected to a gate electrode of thedriving transistor (DR). The switching transistor (ST) supplies a datasignal supplied to the data line (DL1) to the driving transistor (DR),according to a gate signal supplied to the gate line (GL1).

Further, the driving transistor (DR) may have a gate electrode connectedto the drain electrode of the switching transistor (ST), a sourceelectrode connected to the OLED, and a drain electrode connected to aline for supplying a power voltage (VDD). The driving transistor (DR)controls the amount of current flowing to the OLED from the powervoltage (VDD), according to a data signal supplied from the switchingtransistor (ST).

The capacitor (C) is connected between the gate electrode of the drivingtransistor (DR) and the OLED. The capacitor (C) stores therein a voltagecorresponding to a data signal supplied to the gate electrode of thedriving transistor (DR), and constantly maintains an ‘ON’ state of thedriving transistor (DR) for a single frame using the stored voltage.

The timing controller 3 generates image data (R′, G′, B′) by convertingimage signals (R, G, B) provided from the outside, and outputs thegenerated image data to the data driving unit 6.

The timing controller 3 generates gate control signals (CNT1) and datacontrol signals (CNT2) from a control signal (CTN) provided from theoutside, and outputs the generated signals to the gate driving unit 5and the data driving unit 6, respectively.

The data driving unit 6 is connected to the plurality of data lines(DL1˜DLm) of the display panel 2, and generates data signals using thedata control signals (CNT2) and the image data (R′, G′, B′) receivedfrom the timing controller 3. The data signals are supplied to theplurality of data lines (DL1˜DLm) of the display panel 2.

The driving voltage generator 4 generates a gate high voltage (Vgh) anda gate low voltage (Vgl), and outputs the generated voltages to the gatedriving unit 5.

The gate driving unit 5 is connected to the plurality of gate lines(GL1˜GLn) of the display panel 2, and generates gate signals using thesignals provided from the driving voltage generator 4 (i.e., the gatehigh voltage (Vgh) and the gate low voltage (Vgl)), according to thegate control signals (CNT1) received from the timing controller 3. Thegate signals are supplied to the plurality of gate lines (GL1˜GLn) ofthe display panel 2.

In the related art organic light emitting display 1, the switchingdevice of the pixel (P), i.e., the switching transistor (ST) and thedriving transistor (DR) are degraded as time lapses, and thus athreshold voltage (Vth) of the switching device is changed.

FIG. 3 is a graph illustrating a brightness change according to athreshold voltage change, in the related art organic light emittingdisplay.

Referring to FIG. 3, in the related art organic light emitting display1, a threshold voltage (Vth) of a switching device of a pixel (P) isgradually increased as time lapses.

As the threshold voltage (Vth) is increased, a non-uniform amount ofcurrent flows to the OLED, even if a data signal of the same level isapplied to the switching device (i.e., the switching transistor ST). Asa result, brightness of the display panel 2 is gradually reduced as timelapses. This may lower a lifespan of the organic light emitting display1.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an organic lightemitting display and a driving method thereof that substantiallyobviates one or more of the problems due to limitations anddisadvantages of the related art.

Therefore, an object of the present invention is to provide an organiclight emitting display capable of preventing lowering of brightness dueto change of a threshold voltage, by providing a gate signal to adisplay panel, after changing a level of the gate signal according to aset time or a set threshold voltage, and a driving method thereof.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof this specification, as embodied and broadly described herein, anorganic light emitting display comprises a display panel including aplurality of gate lines, a plurality of data line, and a plurality ofpixels disposed at intersections between the gate lines and the datalines, wherein the pixel is provided with a switching transistor, adriving transistor and an organic light emitting diode; a drivingvoltage generator configured to sense a threshold voltage at each pixelof the display panel, and to output a gate high voltage aftercontrolling a level of an original gate high voltage according to alevel of the threshold voltage; and a gate driving unit configured togenerate a gate signal according to a level-controlled gate high voltageoutput from the driving voltage generator, and to supply the generatedgate signal to the switching transistor through the gate lines.

In another aspect, an organic light emitting display comprises a displaypanel including a plurality of gate lines, a plurality of data line, aplurality of sensing lines, and a plurality of pixels disposed atintersections between the gate lines and the data lines, wherein thepixel is provided with a switching transistor, a driving transistor, asensing transistor and an organic light emitting diode; a drivingvoltage generator configured to count an operation time of the displaypanel, and to output a gate high voltage after controlling a level of anoriginal gate high voltage according to the counted operation time; agate driving unit configured to generate a gate signal according to alevel-controlled gate high voltage output from the driving voltagegenerator, and to supply the generated gate signal to the switchingtransistor through the gate lines; and a light emission controllerconfigured to generate a light emission signal according to thelevel-controlled gate high voltage output from the driving voltagegenerator, and to supply the generated light emission signal to thesensing transistor through the sensing lines.

In yet another aspect, a method of driving an organic light emittingdisplay comprises sensing a threshold voltage from a display panelincluding pixels disposed at intersections between a plurality of gatelines and a plurality of data lines, each pixel provided with aswitching transistor, a driving transistor, a sensing transistor and anorganic light emitting diode; comparing the threshold voltage with areference voltage, and outputting a comparison result; and controlling alevel of an original gate high voltage according to the comparisonresult, and outputting a level-controlled gate high voltage.

In a further aspect, a method of driving an organic light emittingdisplay comprises counting an operation time of a display panelincluding pixels disposed at intersections between a plurality of gatelines and a plurality of data lines, each pixel provided with aswitching transistor, a driving transistor, a sensing transistor and anorganic light emitting diode; comparing the counted operation time witha reference time, and outputting a coefficient value; and controlling alevel of a gate high voltage according to the coefficient value, andoutputting a level-controlled gate high voltage.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate exemplary embodiments andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a view illustrating a configuration of an organic lightemitting display in accordance with the related art;

FIG. 2 is an equivalent circuit diagram with respect to a single pixelof FIG. 1;

FIG. 3 is a graph illustrating a brightness change according to athreshold voltage change, in a related art organic light emittingdisplay;

FIG. 4 is a view illustrating a configuration of an organic lightemitting display according to an embodiment of the present invention;

FIG. 5 is a view illustrating a detailed configuration of a voltagecontroller of FIG. 4;

FIG. 6 is a flowchart illustrating operations of the organic lightemitting display of FIG. 4 according to an embodiment of the presentinvention;

FIG. 7 is a flowchart illustrating operations of the organic lightemitting display of FIG. 4 according to another embodiment of thepresent invention;

FIG. 8 is a view illustrating a configuration of an organic lightemitting display according to another embodiment of the presentinvention;

FIG. 9 is a view illustrating a detailed configuration of a voltagecontroller of FIG. 8;

FIG. 10 is a flowchart illustrating operations of the organic lightemitting display of FIG. 8 according to an embodiment of the presentinvention;

FIG. 11 is a flowchart illustrating operations of the organic lightemitting display of FIG. 8 according to another embodiment of thepresent invention;

FIG. 12 is a flowchart illustrating operations of the organic lightemitting display of FIG. 8 according to still another embodiment of thepresent invention; and

FIG. 13 is a graph illustrating that brightness of a display panel isincreased by compensating for a threshold voltage according to anoperation time, in an organic light emitting display according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Description will now be given in detail to example embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

Hereinafter, an organic light emitting display and a driving methodthereof according to the present invention will be explained in moredetail with reference to the attached drawings.

FIG. 4 is a view illustrating a configuration of an organic lightemitting display according to an embodiment of the present invention.

Referring to FIG. 4, an organic light emitting display according to anembodiment of the present invention 100 may include a display panel 110,a timing controller 120, a driving voltage generator 130, a gate drivingunit 150, and a data driving unit 160.

The display panel 110 is an organic light emitting panel where an imageis displayed, and a plurality of gate lines (GL1˜GLn) and a plurality ofdata lines (DL1˜DLm) may be formed to cross each other on the displaypanel 110. A pixel (P) may be formed at each intersection between theplurality of gate lines (GL1˜GLn) and the plurality of data lines(DL1˜DLm).

The pixel (P) may have a 2T(transistor)1C(Capacitor) structure, wheretwo switching devices (i.e., a switching transistor (ST) and a drivingtransistor (DR)), a single capacitor (C) and a single organic lightemitting diode (OLED) are formed.

The switching transistor (ST) of the pixel (P) may have a gate electrodeconnected to a gate line (GL), a source electrode connected to a dataline (DL), and a drain electrode connected to a driving transistor (DR).

Further, the driving transistor (DR) may have a gate electrode connectedto the drain electrode of the switching transistor (ST), a sourceelectrode connected to the OLED, and a drain electrode connected to apower voltage (VDD).

The capacitor (C) of the pixel (P) may be connected between the gateelectrode of the driving transistor (DR) and the OLED.

The switching transistor (ST) of the pixel (P) is turned on by a gatesignal supplied to the gate line (GL), and the capacitor (C) is chargedby a data signal supplied to the data line (DL). The amount of currentflowing on a channel of the driving transistor (DR) may be determinedaccording to a potential difference between a voltage charged to thecapacitor (C) and the power voltage (VDD). And the amount of light to beemitted may be determined by the determined amount of current, so thatthe OLED can emit light.

That is, the switching transistor (ST) of the pixel (P) may serve as aswitching device for supplying a data signal to the driving transistor(DR), and the driving transistor (DT) of the pixel (P) may serve as adriving device for driving the OLED according to a data signal.

The aforementioned display panel 110 may be formed by forming gate lines(GL1˜GLn), data lines (DL1˜DLm) and pixels (P) on a first substratethrough processes such as deposition and photolithography, and byattaching a second substrate onto the first substrate.

The timing controller 120 may generate gate control signals (CNT1) anddata control signals (CNT2) from a control signal (CNT) provided fromthe outside, and may output the gate control signals (CNT1) and the datacontrol signals (CNT2) to the gate driving unit 150 and the data drivingunit 160, respectively.

For instance, a control signal (CNT), such as a vertical synchronizationsignal, a horizontal synchronization signal, a clock signal and a dataenable signal, may be provided to the timing controller 120 from theoutside. The timing controller 120 may generate gate control signals(CNT1) including a start signal, a shift signal, an output enablesignal, etc., from the control signal (CNT), and may output thegenerated gate control signals (CNT1) to the gate driving unit 150.Further, the timing controller 120 may generate data control signals(CNT2) including a start signal, a sampling signal, an output enablesignal, etc., from the control signal (CNT), and may output thegenerated data control signals (CNT2) to the data driving unit 160.

The timing controller 120 may convert image signals (R, G, B) providedfrom the outside, into image data (R′, G′, B′), and may output the imagedata (R′, G′, B′) to the data driving unit 160.

The driving voltage generator 130 may generate a plurality of drivingvoltages such as a gate high voltage (Vgh), a gate low voltage (Vgl) anda common voltage (Vcom), from an operating voltage (Vd) provided fromthe outside. The driving voltage generator 130 may output a gate highvoltage (Vgh) and a gate low voltage (Vgl), to the gate driving unit150.

The driving voltage generator 130 may further include a voltagecontroller 140. The voltage controller 140 may generate a gate highvoltage (Vgh) from an operating voltage (Vd), according to a controlsignal provided from the outside, e.g., an enable signal (En). Then, thevoltage controller 140 may output the generated gate high voltage (Vgh)after controlling a level of the gate high voltage (Vgh) according to acondition.

The reason why the voltage controller 140 outputs a gate high voltage(Vgh) after controlling a level of the gate high voltage (Vgh) accordingto a condition, is in order to prevent degradation of an OLED bycompensating for change of a threshold voltage (Vth) of the switchingtransistor (ST) at each pixel (P) of the display panel 110. Aconfiguration and an operation of the voltage controller 140 will beexplained later in more detail.

The gate driving unit 150 may generate gate signals, from a gate highvoltage (Vgh) and a gate low voltage (Vgl) output from the drivingvoltage generator 130, according to gate control signals (CNT1) outputfrom the timing controller 120. The generated gate signals may besequentially output to the plurality of gate lines (GL1˜GLn) of thedisplay panel 110.

Once the gate high voltage (Vgh) is output after its level has beencontrolled by the voltage controller 140, the gate driving unit 150 maygenerate a gate signal after a level control, in correspondence to thelevel control of the gate high voltage (Vgh).

The data driving unit 160 may generate data signals using image data(R′, G′, B′), according to data control signals (CNT2) output from thetiming controller 120. The generated data signals may be output to theplurality of data lines (DL1˜DLm) of the display panel 110.

The organic light emitting display 100 according to this embodiment mayfurther include a gamma voltage generator (not shown). The gamma voltagegenerator may generate a plurality of gamma voltages, and may output thegenerated gamma voltages to the data driving unit 160. The data drivingunit 160 may generate data signals from image data (R′, G′, B′),according to the generated gamma voltages. The gamma voltages may becomposed of positive voltages and negative voltages.

FIG. 5 is a view illustrating a detailed configuration of the voltagecontroller 140 of FIG. 4.

Referring to FIGS. 4 and 5, the voltage controller 140 may be composedof three modules, e.g., a sensing module 141, a driving time checkmodule 145 and a voltage control module 149.

The sensing module 141 may sense a threshold voltage (Vth) of thedisplay panel 110, thereby outputting a predetermined comparison result(CR). The sensing module 141 may include a sensing unit 142, acomparison unit 144 and a memory 143.

The sensing unit 142 may sense a threshold voltage (Vth) from each pixel(P) of the display panel 110, i.e., a threshold voltage (Vth) from theswitching transistor (ST) of each pixel (P).

The sensing unit 142 may sense a threshold voltage (Vth) at intervals ofevery frame or at intervals of a predetermined number of frames of thedisplay panel 110.

The comparison unit 144 may compare the threshold voltage (Vth) sensedby the sensing unit 142, with a reference voltage (Vref). The referencevoltage (Vref) may be a voltage stored in the memory 143, which may be athreshold voltage of the display panel 110 sensed by the sensing unit142 at a previous sensing operation.

The comparison unit 144 may compare the threshold voltage (Vth) with thereference voltage (Vref), thereby outputting a comparison result (CR).For instance, if the threshold voltage (Vth) is greater than thereference voltage (Vref), the comparison unit 144 may output acomparison result (CR). The comparison result (CR) output from thecomparison unit 144 may be a pulse having a first level, e.g., apositive (+) level.

The memory 143 may store therein the threshold voltage (Vth) sensed bythe sensing unit 142. The stored threshold voltage (Vth) may be used asa reference voltage (Vref) when the comparison unit 144 performs a nextcomparison process.

The driving time check module 145 may count an operation time of thedisplay panel 110, and may output a predetermined coefficient value (TR)from the counted operation time. The driving time check module 145 mayinclude a time setting unit 146 and a counter 147.

In the time setting unit 146, a reference time (Tref) set by a user isstored.

For instance, a user may set one or more reference times (Tref) among atotal operation time of the display panel 110. The reference time (Tref)may be an accumulated operation time of the display panel 110, set inunit of hours, e.g., 100 hours, 1000 hours, etc.

The counter 147 may count an operation time of the display panel 110.The counter 147 may count an operation time of the display panel 110, inunit of hours. That is, the counter 147 may count time taken from aninitial time point when an image is displayed as each pixel (P) of thedisplay panel 110 is operated, to a time point when the operation of thedisplay panel 110 is completed, in an accumulated manner.

If the counted operation time of the display panel 110 is equal to orgreater than the reference time (Tref) provided from the time settingunit 146, the counter 147 may output a predetermined coefficient value(TR). The coefficient value (TR) may be a total operation time of thedisplay panel 110 counted by the counter 147.

The driving time check module 145 may be configured to use a timer (notshown). For instance, the driving time check module 145 may check anoperation time of the display panel 110 using a timer, and may output asignal such as an alarm from the timer, when the checked operation timeis equal to or greater than the reference time (Tref) set by a user.

One of the sensing module 141 and the driving time check module 145 maybe operated, or both of the sensing module 141 and the driving timecheck module 145 may be operated, according to a control signal providedfrom the outside, e.g., an enable signal (En) provided from the timingcontroller 120.

The voltage control module 149 may generate a gate high voltage (Vgh)after controlling a level of the gate high voltage (Vgh), from anoperating voltage (Vd) provided from the outside. Such voltage controlmodule 149 may be a gate high voltage generator 149.

The gate high voltage generator 149 may generate a level-controlled gatehigh voltage (Vgh), from an operating voltage (Vd), according to acomparison result (CR) output from the sensing module 141, or acoefficient value (TR) output from the driving time check module 145.Then, the gate high voltage generator 149 may output the generatedlevel-controlled gate high voltage (Vgh).

The gate high voltage generator 149 may output a gate high voltage (Vgh)reduced in level than the original gate high voltage, according to acomparison result (CR) or a coefficient value (TR).

The level-reduced gate high voltage (Vgh) output from the gate highvoltage generator 149 is provided to the gate driving unit 150. The gatedriving unit 150 generates a gate signal using the gate high voltage(Vgh). In this instance, the gate driving unit 150 may generate a gatesignal reduced in level than the original gate signal. Then, the gatedriving unit 150 may output the generated gate signal to the switchingtransistor (ST) of each pixel (P), through the gate line (GL) of thedisplay panel 110.

Hereinafter, an operation of the organic light emitting display 100including the aforementioned voltage controller 140 according to anembodiment of the present invention, will be explained in more detailwith reference to the attached drawings.

FIG. 6 is a flowchart illustrating operations of the organic lightemitting display of FIG. 4 according to an embodiment of the presentinvention.

Referring to FIGS. 4 to 6, the voltage controller 140 of the drivingvoltage generator 130 may sense a threshold voltage (Vth) at each pixel(P) of the display panel 110 (S11).

For instance, the sensing module 141 of the voltage controller 140 maybe operated by an enable signal (En) provided from the timing controller120. The sensing unit 142 of the sensing module 141 may sense athreshold voltage (Vth) of the switching transistor (ST) at each pixel(P).

Then, the sensed threshold voltage (Vth) is provided to the comparisonunit 144, and the comparison unit 144 may compare the threshold voltage(Vth) with a reference voltage (Vref) (S13).

In this case, the comparison unit 144 may use a threshold voltagepreviously-sensed to be stored in the memory 143, as the referencevoltage (Vref).

If the sensed threshold voltage (Vth) is greater than the referencevoltage (Vref) as a comparison result (Y), the comparison unit 144 mayoutput a comparison result (CR). The comparison result (CR) may beoutput to the gate high voltage generator 149.

The comparison unit 144 may output the comparison result (CR) when thethreshold voltage (Vth) is greater than the reference voltage (Vref) bya predetermined level. For instance, when the threshold voltage (Vth) isgreater than the reference voltage (Vref) by a positive integer (+)(e.g., 1V, 2V, etc.), the comparison unit 144 may output the comparisonresult (CR).

The gate high voltage generator 149 may generate a gate high voltage(Vgh) from an operating voltage (Vd), according to the comparison result(CR) output from the comparison unit 144. The generated gate highvoltage (Vgh) may be reduced in level than the original gate highvoltage (S17).

The gate high voltage generator 149 may generate a gate high voltage(Vgh) reduced in level than the original gate high voltage by apredetermined level. The gate high voltage generator 149 may generate agate high voltage (Vgh) reduced in level than the original gate highvoltage by a negative integer (−) (e.g., −1V, −2V, etc.). In this case,a data signal of the level-reduced gate high voltage (Vgh) may influenceon the amount of current charged to the capacitor (C) of the pixel (P).Therefore, the gate high voltage generator 149 should generate alevel-reduced gate high voltage (Vgh) with consideration of the amountof a data signal to be charged.

The gate high voltage (Vgh) generated from the gate high voltagegenerator 149 may be output to the gate driving unit 15 o, and the gatedriving unit 150 may generate a gate signal reduced in level than theoriginal gate signal using the generated gate high voltage (Vgh). Thelevel-reduced gate signal may be output to the switching transistor (ST)of each pixel (P), through the gate line (GL) of the display panel 110.

That is, in this embodiment, a level of a gate signal provided to a gateelectrode of a switching transistor (ST) of each pixel (P) is controlledaccording to a level of a threshold voltage (Vth) sensed by theswitching transistor (ST). As a result, a change of the thresholdvoltage (Vth) of the switching transistor (ST) can be compensated, andthus the amount of current provided to the OLED can be increased. Thiscan increase brightness of the display panel 110, and preventdegradation of each pixel (P), thereby increasing a lifespan of theorganic light emitting display 100.

If the sensed threshold voltage (Vth) is smaller than the referencevoltage (Vref) as a comparison result by the comparison unit 144 (N),the sensed threshold voltage (Vth) may be stored in the memory 143(S15). The stored threshold voltage (Vth) may be used as a referencevoltage (Vref) when the comparison unit 144 performs a next comparisonprocess.

In this embodiment, the display panel 110 of the sensing module 141senses a threshold voltage (Vth) of the switching transistor (ST) ateach pixel (P). However, the present invention is not limited to this.That is, the sensing module 141 may sense a threshold voltage of thedriving transistor (DR) at each pixel (P) of the display panel 110, andmay output a comparison result. And a level of a gate signal supplied tothe switching transistor (ST) may be controlled according to thecomparison result.

FIG. 7 is a flowchart illustrating operations of the organic lightemitting display of FIG. 4 according to another embodiment of thepresent invention.

Referring to FIGS. 4, 5 and 7, the voltage controller 140 of the drivingvoltage generator 130 may count an operation time of the display panel110 (S21).

The driving time check module 145 of the voltage controller 140 may beoperated according to an enable signal (En) provided from the timingcontroller 120. The counter 147 of the driving time check module 145 maycount an operation time of the display panel 110 from an initialoperation time point, in unit of hours.

The counted operation time may be compared with a reference time (Tref)stored in the time setting unit 146 (S23).

If the counted operation time is greater than or equal to the referencetime (Tref) as a comparison result (Y), the counter 147 may output acoefficient value (TR). The coefficient value (TR) may be a countedoperation time of the display panel 110. The coefficient value (TR) maybe output to the gate high voltage generator 149.

The gate high voltage generator 149 may generate a gate high voltage(Vgh) from an operating voltage (Vd), according to the coefficient value(TR) output from the counter 147. The generated gate high voltage (Vgh)may be a voltage reduced in level than the original gate high voltage(S27).

The gate high voltage generator 149 may generate a gate high voltage(Vgh) reduced in level than the original gate high voltage by apredetermined value. For instance, the gate high voltage generator 149may generate a gate high voltage (Vgh) reduced in level than theoriginal gate high voltage by an integer, e.g., a negative integer (−)such as −1V and −2V.

The gate high voltage (Vgh) generated from the gate high voltagegenerator 149 may be output to the gate driving unit 150, and the gatedriving unit 150 may generate a gate signal reduced in level than theoriginal gate signal, using the generated gate high voltage (Vgh). Thegenerated gate signal may be output to the switching transistor (ST) ofeach pixel (P), through the gate line (GL) of the display panel 110.

That is, in this embodiment, a level of a gate signal provided to a gateelectrode of a switching transistor (ST) of each pixel (P) is controlledaccording to an operation time of the organic light emitting display100. As a result, a threshold voltage (Vth) of the switching transistor(ST), which is variable according to an operation time of the organiclight emitting display 100, can be compensated. Therefore, the amount ofcurrent provided to the OLED can be increased. This can increasebrightness of the display panel 110, prevent degradation of each pixel(P), and increase a lifespan of the organic light emitting display 100.

If the counted operation time is smaller than the reference time (Tref)as a comparison result (N), the counter 147 may store the countedoperation time of the display panel 110 by accumulating a coefficientvalue (TR) at a next counting operation (S25).

FIG. 8 is a view illustrating a configuration of an organic lightemitting display according to another embodiment of the presentinvention.

Referring to FIG. 8, the organic light emitting display according toanother embodiment of the present invention 101 may include a displaypanel 111, a timing controller 121, a driving voltage generator 131, agate driving unit 150, a light emission controller 170, and a datadriving unit 160.

The display panel 111 is an organic light emitting panel, and aplurality of gate lines (GL1˜GLn) and a plurality of data lines(DL1˜DLm) may be formed at the display panel 111 so as to cross eachother. A pixel (P) may be formed at each intersection between theplurality of gate lines (GL1˜GLn) and the plurality of data lines(DL1˜DLm).

A plurality of sensing lines (SL1˜SLn) having the same number as theplurality of gate lines (GL1˜GLn) may be formed at the display panel 111in parallel to the plurality of gate lines (GL1˜GLn).

The pixel (P) may have a 3T(Transistor)1C(Capacitor) structure, wherethree switching devices (i.e., a switching transistor (ST1), a drivingtransistor (DR), and a sensing transistor (ST2)), a single capacitor (C)and a single organic light emitting diode (OLED) are formed.

The switching transistor (ST1) of the pixel (P) may have a gateelectrode connected to the gate line (GL), a source electrode connectedto the data line (DL), and a drain electrode connected to the drivingtransistor (DR).

Further, the driving transistor (DR) may have a gate electrode connectedto the drain electrode of the switching transistor (ST1), a sourceelectrode connected to the OLED, and a drain electrode connected to apower voltage (VDD).

The sensing transistor (ST2) of the pixel (P) may have a gate electrodeconnected to the sensing line (SL), a source electrode connected to thesource electrode of the driving transistor (DR), and a drain electrodeconnected to a ground voltage (VSS).

The capacitor (C) of the pixel (P) may be connected between the gateelectrode of the driving transistor (DR) and the OLED.

The switching transistor (ST) of the pixel (P) is turned on by a gatesignal supplied to the gate line (GL), and the capacitor (C) is chargedby a data signal supplied to the data line (DL). The amount of currentflowing on a channel of the driving transistor (DR) may be determinedaccording to a potential difference between a voltage charged to thecapacitor (C) and the power voltage (VDD). And the amount of light to beemitted may be determined by the determined amount of current, so thatthe OLED can emit light. In this case, the sensing transistor (ST2) isturned on by a sensing signal provided through the sensing line (SL),and can prevent the OLED from emitting light by the power voltage (VDD),before the capacitor (C) is charged by a data signal during an initialoperation of the switching transistor (ST1).

The timing controller 121 may generate a gate control signal (CNT1), adata control signal (CTN2) and a light emission control signal (CNT3),from a control signal (CNT) provided from the outside, and may outputthe generated signals to the gate driving unit 150, the data drivingunit 160 and the light emission controller 170, respectively.

The timing controller 121 may convert image signals (R, G, B) providedfrom the outside, into image data (R′, G′, B′), and may output the imagedata (R′, G′, B′) to the data driving unit 160.

The driving voltage generator 131 may generate a plurality of drivingvoltages, e.g., a gate high voltage such as a first gate high voltage(Vgh) and a second gate high voltage (Vgh′), a gate low voltage (Vgl), acommon voltage (Vcom), etc., from an operating voltage (Vd) providedfrom the outside. Then, the driving voltage generator 131 may output thegenerated driving voltages.

The driving voltage generator 131 may output the first gate high voltage(Vgh) and the gate low voltage (Vgl) to the gate driving unit 150, andmay output the second gate high voltage (Vgh′) and the gate low voltage(Vgl) to the light emission controller 170.

The driving voltage generator 131 may further include a voltagecontroller 200. The voltage controller 200 may generate the first gatehigh voltage (Vgh) and the second gate high voltage (Vgh′), from anoperating voltage (Vd), according to a control signal (e.g., an enablesignal (En)). Then, the voltage controller 200 may output the generatedvoltages.

In this case, the voltage controller 200 may output the first gate highvoltage (Vgh) and the second gate high voltage (Vgh′), after controllingtheir levels according to a condition.

The reason why the voltage controller 200 outputs the first gate highvoltage (Vgh) and the second gate high voltage (Vgh′), after controllingtheir levels according to a condition, is in order to preventdegradation of an OLED by compensating for change of a threshold voltage(Vth) of the switching transistor (ST1) and the sensing transistor (ST2)at each pixel (P) of the display panel 110. A configuration and anoperation of the voltage controller 200 will be explained later in moredetail.

The gate driving unit 150 may generate a gate signal, from the firstgate high voltage (Vgh) and the gate low voltage (Vgl) output from thedriving voltage generator 131, according to the gate control signal(CNT1) provided from the timing controller 121. The generated gatesignal may be sequentially output to the plurality of gate lines(GL1˜GLn) of the display panel 111.

Once the first gate high voltage (Vgh) is output after its level hasbeen controlled by the voltage controller 200, the gate driving unit 150may generate a gate signal after a level control in correspondence tothe level control of the first gate high voltage (Vgh).

The data driving unit 160 may generate a data signal using the imagedata (R′, G′, B′), according to the data control signal (CTN2) providedfrom the timing controller 121. The generated data signal may be outputto the plurality of data lines (DL1˜DLm) of the display panel 111.

The light emission controller 170 may generate a light emission signal,from the second gate high voltage (Vgh′) and the gate low voltage (Vgl)output from the driving voltage generator 131, according to the lightemission control signal (CNT3) provided from the timing controller 121.The generated light emission signal may be sequentially output to theplurality of sensing lines (SL1˜SLn) of the display panel 111.

Once the second gate high voltage (Vgh′) is output after its level hasbeen controlled by the voltage controller 200, the light emissioncontroller 170 may generate a light emission signal after a levelcontrol in correspondence the level control of the second gate highvoltage (Vgh′).

The organic light emitting display 101 according to this embodiment mayfurther include a gamma voltage generator (not shown). The gamma voltagegenerator may generate a plurality of gamma voltages, and may output thegenerated gamma voltages to the data driving unit 160. The data drivingunit 160 may generate data signals from image data (R′, G′, B′),according to the generated gamma voltages. The gamma voltages may becomposed of positive voltages and negative voltages.

FIG. 9 is a view illustrating a detailed configuration of the voltagecontroller of FIG. 8.

Referring to FIGS. 8 and 9, the voltage controller 200 may be composedof three modules, i.e., a sensing module 210, a driving time checkmodule 220 and a voltage control module 230.

The sensing module 210 may sense a first threshold voltage (Vth1) and asecond threshold voltage (Vths) from the display panel 111, and mayoutput each comparison result (CR). The sensing module 210 may include afirst sensing unit 211, a second sensing unit 213, a comparison unit215, and a memory 217.

The first sensing unit 211 may sense a threshold voltage from theswitching transistor (ST1) (i.e., a first threshold voltage Vth1) fromeach pixel (P) of the display panel 111. The second sensing unit 213 maysense a threshold voltage from the sensing transistor (ST2) (i.e., asecond threshold voltage Vth2) from each pixel (P) of the display panel111.

The first sensing unit 211 and the second sensing unit 213 may sense thefirst threshold voltage Vth1 and the second threshold voltage Vth2 atintervals of every frame or at intervals of a predetermined number offrames of the display panel 111. One of the first sensing unit 211 andthe second sensing unit 213 may be operated, or both of the firstsensing unit 211 and the second sensing unit 213 may be operated.

The comparison unit 215 may compare the first threshold voltage (Vth1)sensed by the first sensing unit 211, with a first reference voltage(Vref1). Further, the comparison unit 215 may compare the secondthreshold voltage (Vth2) sensed by the second sensing unit 213, with asecond reference voltage (Vref2).

The first reference voltage (Vref1) may be a threshold voltage sensed bythe first sensing unit 211 based on a previous sensing operation, andthe second reference voltage (Vref2) may be a threshold voltage sensedby the second sensing unit 213 based on a previous sensing operation.

The comparison unit 215 may compare the first threshold voltage (Vth1)with the first reference voltage (Vref1), thereby outputting a firstcomparison result (CR1). For instance, when the first threshold voltage(Vth1) is larger than the first reference voltage (Vref1), thecomparison unit 215 may output a first comparison result (CR1).

The comparison unit 215 may compare the second threshold voltage (Vth2)with the second reference voltage (Vref2), thereby outputting a secondcomparison result (CR2). For instance, when the second threshold voltage(Vth2) is larger than the second reference voltage (Vref2), thecomparison unit 215 may output a second comparison result (CR2).

Each of the first comparison result (CR1) and the second comparisonresult (CR2) may be a pulse having a first level, e.g., a positive (+)level.

The memory 217 may store therein the first threshold voltage (Vth1) andthe second threshold voltage (Vth2) sensed by the first sensing unit 211and the second sensing unit 213. The stored first threshold voltage(Vth1) and second threshold voltage (Vth2) may be used as the firstreference voltage (Vref1) and the second reference voltage (Vref2) whenthe comparison unit 215 performs a next comparison process,respectively.

The driving time check module 220 may count an operation time of thedisplay panel 111, and may output a predetermined coefficient value (TR)from the counted operation time. The driving time check module 220 mayinclude a time setting unit 223 and a counter 221.

In the time setting unit 223, a reference time (Tref) set by a user isstored.

For instance, a user may set one or more reference times (Tref) among atotal operation time of the display panel 111. The reference time (Tref)may be an accumulated operation time of the display panel 111, set inunit of hours, e.g., 100 hours, 1000 hours, etc.

The counter 221 may count an operation time of the display panel 111.The counter 221 may count an operation time of the display panel 111, inunit of hours. That is, the counter 221 may count time taken from aninitial time point when an image is displayed as each pixel (P) of thedisplay panel 111 is operated, to a time point when the operation of thedisplay panel 111 is completed, in an accumulated manner.

If the counted operation time of the display panel 111 is equal to orgreater than the reference time (Tref) provided from the time settingunit 223, the counter 221 may output a predetermined coefficient value(TR). The coefficient value (TR) may be a total operation time of thedisplay panel 111 counted by the counter 221.

The driving time check module 220 may be configured to use a timer (notshown). For instance, the driving time check module 220 may check anoperation time of the display panel 111 using a timer, and may output asignal such as an alarm from the timer, when the checked operation timeis equal to or greater than the reference time (Tref) set by a user.

One of the sensing module 210 and the driving time check module 220 maybe operated, or both of the sensing module 210 and the driving timecheck module 220 may be operated, according to a control signal providedfrom the outside, e.g., an enable signal (En) provided from the timingcontroller 121.

The voltage control module 230 may generate a gate high voltage, e.g., afirst gate high voltage (Vgh) and a second gate high voltage (Vgh′),from an operating voltage (Vd) provided from the outside, after a levelcontrol. The voltage control module 230 may include a first gate highvoltage generator 231 and a second gate high voltage generator 233.

The first gate high voltage generator 231 may generate alevel-controlled first gate high voltage (Vgh), from an operatingvoltage (Vd), according to a first comparison result (CR1) output fromthe sensing module 210, or a coefficient value (TR) output from thedriving time check module 220. Then, the first gate high voltagegenerator 231 may output the generated level-controlled first gate highvoltage (Vgh).

That is, the first gate high voltage generator 231 may generate a firstgate high voltage (Vgh) reduced in level than the original gate highvoltage, according to a first comparison result (CR1) or a coefficientvalue (TR), and may output the first gate high voltage (Vgh).

The level-reduced first gate high voltage (Vgh) output from the firstgate high voltage generator 231 may be provided to the gate driving unit150. The gate driving unit 150 may generate a gate signal, using thefirst gate high voltage (Vgh). In this instance, the gate driving unit150 may generate a gate signal reduced in level than the original gatesignal. Then, the gate driving unit 150 may output the generated gatesignal to the switching transistor (ST1) of each pixel (P), through thegate line (GL) of the display panel 111.

The second gate high voltage generator 233 may generate alevel-controlled second gate high voltage (Vgh′), from an operatingvoltage (Vd), according to a second comparison result (CR2) output fromthe sensing module 210, or a coefficient value (TR) output from thedriving time check module 220. Then, the second gate high voltagegenerator 233 may output the generated level-controlled second gate highvoltage (Vgh′).

That is, the second gate high voltage generator 233 may generate asecond gate high voltage (Vgh′) increased in level than the originalgate high voltage, according to a second comparison result (CR2) or acoefficient value (TR). Then, the second gate high voltage generator 233may output the generated second gate high voltage (Vgh′).

The level-increased second gate high voltage (Vgh′) output from thesecond gate high voltage generator 233 may be provided to the lightemission controller 170. The light emission controller 170 may generatea light emission signal, using the second gate high voltage (Vgh′). Inthis instance, the light emission controller 170 may generate a lightemission signal increased in level than the original light emissionsignal. The light emission controller 170 may output the generated lightemission signal to the sensing transistor (ST2) of each pixel (P),through the sensing line (SL) of the display panel 111.

Hereinafter, an operation of the organic light emitting display 101including the voltage controller 200, according to another embodiment ofthe present invention will be explained in more detail with reference tothe attached drawings.

FIG. 10 is a flowchart illustrating operations of the organic lightemitting display of FIG. 8 according to an embodiment of the presentinvention.

Referring to FIGS. 8 to 10, the voltage controller 200 of the drivingvoltage generator 131 may sense a threshold voltage of the switchingtransistor (ST1), i.e., a first threshold voltage (Vth1), at each pixel(P) of the display panel 111 (S31).

For instance, the sensing module 210 of the voltage controller 200 maybe operated by an enable signal (En) provided from the timing controller121. The first sensing unit 211 of the sensing module 210 may sense athreshold voltage of the switching transistor (ST1), i.e., a firstthreshold voltage (Vth1), at each pixel (P) of the display panel 111.

Then, the sensed first threshold voltage (Vth1) is provided to thecomparison unit 215, and the comparison unit 215 may compare the firstthreshold voltage (Vth1) with a first reference voltage (Vref1) (S33).

In this case, the first reference voltage (Vref1) may be a voltagestored in the memory 217 of the sensing module 210, which may be athreshold voltage of the switching transistor ST1 sensed by the firstsensing unit 211 at a previous sensing operation.

If the first threshold voltage (Vth1) is greater than the firstreference voltage (Vref1) as a comparison result (Y), the comparisonunit 215 may output a first comparison result (CR1). The firstcomparison result (CR1) may be output to the voltage control module 230.

The comparison unit 215 may output the first comparison result (CR1)when the first threshold voltage (Vth1) is greater than the firstreference voltage (Vref1) by a predetermined level, e.g., a positiveinteger (+).

The first gate high voltage generator 231 of the voltage control module230 may generate a first gate high voltage (Vgh) from an operatingvoltage (Vd), according to the first comparison result (CR1) output fromthe comparison unit 215. The generated first gate high voltage (Vgh) maybe reduced in level than the original first gate high voltage (S37).

The first gate high voltage generator 231 of the voltage control module230 may generate a first gate high voltage (Vgh) according to the firstcomparison result (CR1). The generated first gate high voltage (Vgh) maybe reduced in level than the original first gate high voltage, by apredetermined level, e.g., a negative integer (−).

The level-reduced first gate high voltage (Vgh) output from the firstgate high voltage generator 231 is provided to the gate driving unit150. The gate driving unit 150 generates a gate signal, using the firstgate high voltage (Vgh). In this instance, the gate driving unit 150 maygenerate a gate signal reduced in level than the original gate signal.Then, the gate driving unit 150 may output the generated gate signal tothe switching transistor (ST1) of each pixel (P), through the gate line(GL) of the display panel 111.

That is, in this embodiment, a level of a gate signal provided to a gateelectrode of a switching transistor (ST1) of each pixel (P) iscontrolled according to a level of a first threshold voltage (Vth1)sensed by the switching transistor (ST1). As a result, a change of thefirst threshold voltage (Vth1) of the switching transistor (ST1) can becompensated, and thus the amount of current provided to the OLED can beincreased. This can increase brightness of the display panel 111, andprevent degradation of each pixel (P), thereby increasing a lifespan ofthe organic light emitting display 101.

If the sensed first threshold voltage (Vth1) is smaller than the firstreference voltage (Vref1) as a comparison result by the comparison unit215 (N), the sensed first threshold voltage (Vth1) may be stored in thememory 217 (S35). The stored first threshold voltage (Vth1) may be usedas a first reference voltage (Vref1) when the comparison unit 215performs a next comparison process.

FIG. 11 is a flowchart illustrating operations of the organic lightemitting display of FIG. 8 according to another embodiment of thepresent invention.

Referring to FIGS. 8, 9 and 11, the voltage controller 200 of thedriving voltage generator 131 may sense a threshold voltage of thesensing transistor (ST2), i.e., a second threshold voltage (Vth2), ateach pixel (P) of the display panel 111 (S41).

For instance, the sensing module 210 of the voltage controller 200 maybe operated by an enable signal (En) provided from the timing controller121. The second sensing unit 213 of the sensing module 210 may sense athreshold voltage of the sensing transistor (ST2), i.e., a secondthreshold voltage (Vth2), at each pixel (P) of the display panel 111.

Then, the sensed second threshold voltage (Vth2) is provided to thecomparison unit 215, and the comparison unit 215 may compare the secondthreshold voltage (Vth2) with a second reference voltage (Vref2) (S43).

In this case, the second reference voltage (Vref2) may be a voltagestored in the memory 217 of the sensing module 210, which may be athreshold voltage of the sensing transistor ST2 sensed by the secondsensing unit 213 at a previous sensing operation.

If the second threshold voltage (Vth2) is greater than the secondreference voltage (Vref2) as a comparison result (Y), the comparisonunit 215 may output a second comparison result (CR2). The secondcomparison result (CR2) may be output to the voltage control module 230.

The comparison unit 215 may output the second comparison result (CR2)when the second threshold voltage (Vth2) is greater than the secondreference voltage (Vref2) by a positive integer (+).

The second gate high voltage generator 233 of the voltage control module230 may generate a second gate high voltage (Vgh′) from an operatingvoltage (Vd), according to the second comparison result (CR2) outputfrom the comparison unit 215. The generated second gate high voltage(Vgh′) may be increased in level than the original second gate highvoltage (S47).

The second gate high voltage generator 233 of the voltage control module230 may generate a second gate high voltage (Vgh′) according to thesecond comparison result (CR2). The generated second gate high voltage(Vgh′) may be increased in level than the original second gate highvoltage, by a positive integer (+).

The second gate high voltage (Vgh′) generated from the second gate highvoltage generator 233 is provided to the light emission controller 170.The light emission controller 170 generates a light emission signal,using the second gate high voltage (Vgh′). In this instance, the lightemission controller 170 may generate a light emission signal increasedin level than the original light emission signal. Then, the lightemission controller 170 may output the generated light emission signalto the sensing transistor (ST2) of each pixel (P), through the sensingline (SL) of the display panel 111.

That is, in this embodiment, a level of a light emission signal providedto a gate electrode of a sensing transistor (ST2) of each pixel (P) iscontrolled according to a level of a second threshold voltage (Vth2)sensed by the sensing transistor (ST2). As a result, change of thesecond threshold voltage (Vth2) of the sensing transistor (ST2) can becompensated, and thus the amount of current provided to the OLED can beincreased. This can increase brightness of the display panel 111, andprevent degradation of each pixel (P), thereby increasing a lifespan ofthe organic light emitting display 101.

If the sensed second threshold voltage (Vth2) is smaller than the secondreference voltage (Vref2) as a comparison result by the comparison unit215 (N), the sensed second threshold voltage (Vth2) may be stored in thememory 217 (S45). The stored second threshold voltage (Vth2) may be usedas a second reference voltage (Vref2) when the comparison unit 215performs a next comparison process.

The configuration to output the first gate high voltage (Vgh)aforementioned with reference to FIG. 10, and the configuration tooutput the second gate high voltage (Vgh′) aforementioned with referenceto FIG. 11 may be implemented together.

For instance, the sensing module 210 may sense a first threshold voltage(Vth1) of the display panel 111, and output a first comparison result(CR1). Alternatively, the sensing module 210 may sense a secondthreshold voltage (Vth2) of the display panel 111, and output a secondcomparison result (CR2). Still alternatively, the sensing module 210 maysense both a first threshold voltage (Vth1) and a second thresholdvoltage (Vth1) of the display panel 111, and output both a firstcomparison result (CR1) and a second comparison result (CR2).

Once the sensing module 210 outputs the first comparison result (CR1) orthe second comparison result (CR2), the voltage control module 230 maygenerate a first gate high voltage (Vgh) reduced in level than theoriginal gate high voltage, and a second gate high voltage (Vgh′)increased in level than the original gate high voltage, according to thefirst comparison result (CR1) or the second comparison result (CR2).Then the voltage control module 230 may output the generated first gatehigh voltage (Vgh) and second gate high voltage (Vgh′)

The first gate high voltage (Vgh) may be output to the gate driving unit150. The gate driving unit 150 may generate a gate signal reduced inlevel according to the first gate high voltage (Vgh), and may output thegenerated gate signal to the switching transistor (ST1) of each pixel(P) of the display panel 111.

The second gate high voltage (Vgh′) may be output to the light emissioncontroller 170. The light emission controller 170 may generate a lightemission signal increased in level according to the second gate highvoltage (Vgh′), and may output the generated light emission signal tothe sensing transistor (ST2) of each pixel (P) of the display panel 111.

FIG. 12 is a flowchart illustrating operations of the organic lightemitting display of FIG. 8 according to still another embodiment of thepresent invention.

Referring to FIGS. 8, 9 and 12, the voltage controller 200 of thedriving voltage generator 131 may sense an operation time of the displaypanel 111 (S51).

The driving time check module 220 of the voltage controller 200 may beoperated according to an enable signal (En) provided from the timingcontroller 121. The counter 221 of the driving time check module 200 maycount an operation time of the display panel 111 from an initialoperation time point, in unit of hours.

The counted operation time may be compared with a reference time (Tref)stored in the time setting unit 223 (S53).

If the counted operation time is greater than or equal to the referencetime (Tref) as a comparison result (Y), the counter 221 may output acoefficient value (TR). The coefficient value (TR) may be a countedoperation time of the display panel 111. The coefficient value (TR) maybe output to the voltage control module 230.

The first gate high voltage generator 231 of the voltage control module230 may generate a first gate high voltage (Vgh) from an operatingvoltage (Vd), according to the coefficient value (TR) output from thecounter 221. The generated first gate high voltage (Vgh) may be avoltage reduced in level than the original gate high voltage (S57).

The second gate high voltage generator 233 of the voltage control module230 may generate a second gate high voltage (Vgh′) from an operatingvoltage (Vd), according to the coefficient value (TR) output from thecounter 221. The generated second gate high voltage (Vgh′) may be avoltage increased in level than the original gate high voltage (S58).

Each of the first gate high voltage (Vgh) and the second gate highvoltage (Vgh′) may be a voltage reduced or increased in level than theoriginal gate high voltage by an integer rather than ‘0’.

The first gate high voltage (Vgh) may be output to the gate driving unit150. The gate driving unit 150 may generate a gate signal reduced inlevel according to the first gate high voltage (Vgh), and may output thegenerated gate signal to the switching transistor (ST1) of each pixel(P) of the display panel 111.

The second gate high voltage (Vgh′) may be output to the light emissioncontroller 170. The light emission controller 170 may generate a lightemission signal increased in level according to the second gate highvoltage (Vgh′), and may output the generated light emission signal tothe sensing transistor (ST2) of each pixel (P) of the display panel 111.

That is, in this embodiment, a level of a gate signal and a lightemission signal provided to each gate electrode of a switchingtransistor (ST1) and a sensing transistor (ST2) of each pixel (P) iscontrolled according to an operation time of the organic light emittingdisplay 101. As a result, threshold voltages of the switching transistor(ST1) and the sensing transistor (ST2), which are variable according toan operation time of the organic light emitting display 101, can becompensated. Therefore, the amount of current provided to the OLED canbe increased. This can increase brightness of the display panel 111,prevent degradation of each pixel (P), and increase a lifespan of theorganic light emitting display 101.

If the counted operation time is smaller than the reference time (Tref)as a comparison result (N), the counter 221 may store the operation timeof the display panel 111 by accumulating a coefficient value (TR) at anext counting operation (S55).

The following tables 1 and 2 show that brightness of a display panel isincreased by compensating for a threshold voltage according to a changeamount of the threshold voltage, in the organic light emitting displayaccording to the present invention.

TABLE 1 Change amount of Vth Vgh 24 V 27 V 1.5 V OLED 2.41E−07 2.51E−07Current Brightness 92.6% 96.1% Ratio

TABLE 2 Change amount of Vth Vgh 27 V 30 V 3.0 V OLED 2.41E−07 2.51E−07Current Brightness 92.6% 96.1% Ratio

As can be seen from the tables 1 and 2, the organic light emittingdisplay according to the present invention can sense a change amount ofa threshold voltage of a switching device at each pixel, and increase alevel of a gate high voltage, thereby having an enhanced brightness.

In the tables 1 and 2, the Vth change amount indicates a change amountof a threshold voltage of a sensing transistor at each pixel, and Vghindicates a gate high voltage for generating a light emission signalprovided to a sensing transistor of each pixel.

As can be seen from the table 1, as a gate high voltage is increased by3V, a level of a light emission signal provided to a sensing transistoris increased, and thus brightness of the organic light emitting displayis increased by 3.8%.

As can be seen from the table 2, as a gate high voltage is increased by3V, a level of a light emission signal provided to a sensing transistoris increased, and thus brightness of the organic light emitting displayis increased by 2.8%.

FIG. 13 is a graph illustrating that brightness of a display panel isincreased by compensating for a threshold voltage according to anoperation time, in an organic light emitting display according to thepresent invention.

As shown in FIG. 13, the organic light emitting display according to thepresent invention can have an enhanced brightness, by controlling alevel of a signal provided to a switching device of each pixel (e.g., aswitching transistor and a sensing transistor of each pixel), byincreasing or reducing a level of a gate high voltage within a setoperation time.

As an example, as a level of a gate high voltage is increased or reducedwithin a set operation of 10,000 hours, a level of a gate signal and alight emission signal provided to a switching transistor and a sensingtransistor, respectively can be increased and reduced. This can enhancebrightness of the organic light emitting display.

As another example, as a level of a gate high voltage is increased orreduced within a set operation of 20,000 hours, a level of a gate signaland a light emission signal provided to a switching transistor and asensing transistor, respectively can be increased and reduced. This canenhance brightness of the organic light emitting display.

As brightness of the organic light emitting display is increased bycontrolling a level of signals provided to the switching transistor andthe sensing transistor, the organic light emitting display can have alifespan (A) increased as compared to a related art lifespan (A′) byabout 19%.

The present invention may have at least the following advantages. As agate signal is provided to a display panel after its level has beenchanged according to a set time or a set threshold voltage, degradationof a pixel due to change of a threshold voltage can be prevented. Theorganic light emitting display of the present invention can have aprolonged a lifespan by preventing lowering of brightness of a displaypanel.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An organic light emitting display, comprising: adisplay panel including a plurality of gate lines, a plurality of dataline, and a plurality of pixels disposed at intersections between thegate lines and the data lines, wherein the pixel is provided with aswitching transistor, a driving transistor and an organic light emittingdiode; a driving voltage generator configured to sense a thresholdvoltage at each pixel of the display panel, and to output a gate highvoltage after controlling a level of an original gate high voltageaccording to a level of the threshold voltage; and a gate driving unitconfigured to generate a gate signal according to a level-controlledgate high voltage output from the driving voltage generator, and tosupply the generated gate signal to the switching transistor through thegate lines.
 2. The organic light emitting display of claim 1, whereinthe driving voltage generator comprises: a sensing module configured tosense the threshold voltage from the switching transistor of each pixel,to compare the threshold voltage with a reference voltage, and to outputa comparison result; and a voltage control module configured to generatea gate high voltage reduced in level than the original gate high voltageaccording to the comparison result, and to output the generated gatehigh voltage.
 3. The organic light emitting display of claim 2, whereinthe reference voltage is a threshold voltage of the switching transistorsensed by the sensing module at a previous sensing operation.
 4. Theorganic light emitting display of claim 2, wherein the sensing moduleoutputs the comparison result when the threshold voltage is greater thanthe reference voltage.
 5. The organic light emitting display of claim 1,further comprising: a plurality of sensing lines disposed in parallel tothe plurality of gate lines of the display panel; a sensing transistordisposed at the pixel, and connected to the sensing line; and a lightemission controller configured to generate a light emission signalaccording to the level-controlled gate high voltage output from thedriving voltage generator, and to supply the light emission signal tothe sensing transistor through the sensing line.
 6. The organic lightemitting display of claim 5, wherein the driving voltage generatorcomprises: a sensing module configured to sense a first thresholdvoltage from the switching transistor of each pixel, to sense a secondthreshold voltage from the sensing transistor of each pixel, to compareat least one of the first and second threshold voltages with a referencevoltage, and to output a comparison result; and a voltage control moduleconfigured to generate at least one of a first gate high voltage reducedin level than the original gate high voltage, and a second gate highvoltage increased in level than the original gate high voltage,according to the comparison result, wherein the voltage control moduleoutputs the first gate high voltage to the gate driving unit, andoutputs the second gate high voltage to the light emission controller.7. The organic light emitting display of claim 6, wherein the referencevoltage includes a first reference voltage and a second referencevoltage, and wherein the sensing module outputs the comparison resultwhen the first threshold voltage is greater than the first referencevoltage, or when the second threshold voltage is greater than the secondreference voltage.
 8. The organic light emitting display of claim 7,wherein the first reference voltage is a threshold voltage of theswitching transistor sensed by the sensing module at a previous sensingoperation, and wherein the second reference voltage is a thresholdvoltage of the sensing transistor sensed by the sensing module at aprevious sensing operation.
 9. An organic light emitting display,comprising: a display panel including a plurality of gate lines, aplurality of data line, a plurality of sensing lines, and a plurality ofpixels disposed at intersections between the gate lines and the datalines, wherein the pixel is provided with a switching transistor, adriving transistor, a sensing transistor and an organic light emittingdiode; a driving voltage generator configured to count an operation timeof the display panel, and to output a gate high voltage aftercontrolling a level of an original gate high voltage according to thecounted operation time; a gate driving unit configured to generate agate signal according to a level-controlled gate high voltage outputfrom the driving voltage generator, and to supply the generated gatesignal to the switching transistor through the gate lines; and a lightemission controller configured to generate a light emission signalaccording to the level-controlled gate high voltage output from thedriving voltage generator, and to supply the generated light emissionsignal to the sensing transistor through the sensing lines.
 10. Theorganic light emitting display of claim 9, wherein the driving voltagegenerator comprises: a driving time check module configured to comparethe counted operation time with a reference time, and to output acoefficient value; and a voltage control module configured to generateat least one of a first gate high voltage reduced in level than theoriginal gate high voltage, and a second gate high voltage increased inlevel than the original gate high voltage, according to the coefficientvalue, wherein the voltage control module outputs the first gate highvoltage to the gate driving unit, and outputs the second gate highvoltage to the light emission controller.
 11. The organic light emittingdisplay of claim 10, wherein the driving time check module outputs thecoefficient value when the counted operation time is equal to or greaterthan the reference time.
 12. A method of driving an organic lightemitting display, the method comprising: sensing a threshold voltagefrom a display panel including pixels disposed at intersections betweena plurality of gate lines and a plurality of data lines, each pixelprovided with a switching transistor, a driving transistor, a sensingtransistor and an organic light emitting diode; comparing the thresholdvoltage with a reference voltage, and outputting a comparison result;and controlling a level of an original gate high voltage according tothe comparison result, and outputting a level-controlled gate highvoltage.
 13. The method of claim 12, wherein the step of sensing athreshold voltage comprises: sensing a first threshold voltage of theswitching transistor of each pixel; and sensing a second thresholdvoltage of the sensing transistor of each pixel.
 14. The method of claim13, wherein when the first threshold voltage is greater than thereference voltage, the comparison result is output, and wherein in thestep of controlling and outputting a level of an original gate highvoltage, a first gate high voltage reduced in level than the originalgate high voltage is generated according to the comparison result, andthe first gate high voltage is output to the switching transistor ofeach pixel.
 15. The method of claim 13, wherein when the secondthreshold voltage is greater than the reference voltage, the comparisonresult is output, and wherein in the step of controlling and outputtinga level of an original gate high voltage, a second gate high voltageincreased in level than the original gate high voltage is generatedaccording to the comparison result, and the second gate high voltage isoutput to the sensing transistor of each pixel.
 16. A method of drivingan organic light emitting display, the method comprising: counting anoperation time of a display panel including pixels disposed atintersections between a plurality of gate lines and a plurality of datalines, each pixel provided with a switching transistor, a drivingtransistor, a sensing transistor and an organic light emitting diode;comparing the counted operation time with a reference time, andoutputting a coefficient value; and controlling a level of an originalgate high voltage according to the coefficient value, and outputting alevel-controlled gate high voltage.
 17. The method of claim 16, whereinwhen the counted operation time is equal to or greater than thereference time, the coefficient result is output, and wherein in thestep of controlling and outputting a level of an original gate highvoltage, a first gate high voltage reduced in level than the originalgate high voltage is generated according to the coefficient value, andthe first gate high voltage is output to the switching transistor ofeach pixel.
 18. The method of claim 16, wherein when the countedoperation time is equal to or greater than the reference time, thecoefficient result is output, and wherein in the step of controlling andoutputting a level of an original gate high voltage, a second gate highvoltage increased in level than the original gate high voltage isgenerated according to the coefficient value, and the second gate highvoltage is output to the sensing transistor of each pixel.